The door to a bedroom is closed 24/7. Someone told me, "Be careful. It sounds like you are pressurizing the room."
The room is fairly pressurized, I suppose; I can feel air rushing out from underneath the bottom of the door if I stand outside the room and in front of the closed door.
But what is bad about that? I don't understand the practical significance of air pressure.
In a properly configured home, the return air ducting is the exit path for airflow. There's no significant pressure buildup in any room regardless of door position.
In older homes without return ducting, or vents solely in common areas, the return air path is indeed through or around the door. Still, pressure buildup is extremely small unless the door is extraordinarily well sealed.
You should probably ask "someone" what his or her concern actually is. The pressure differential in your situation is miniscule--probably not even enough to pop your ears. The only downside I can come up with is the accumulation of dust bunnies outside your door.
A typical interior doorway has a gap of about 3mm along each side and the top, and often 5-10mm underneath. This gives an area of around 20,000 mm^2, or about the same area as 150mm (6") duct. Unless you take action to prevent airflow through these gaps (e.g. installing draft excluders or an automatic door closer that pushes the door tightly against the frame), you will not see a noticeable build-up of pressure. Now the gap around a door does not exactly provide an unobstructed path for air flow, but even assuming a high friction coefficient for air leaking through the doorway, a 0.05kPa pressure difference (which is very small) would cause about 0.5 to 1 cubic metre (about 15-30 cubic feet) of air flow per minute. Your room will still get adequate ventilation, and you won't find a noticeable pressure change between the two sides of the door.
If your forced air HVAC system does not have return ducts or if the return in this room is too restrictive, then the return air must flow under the door to a hallway and down to the hallway HVAC intake. If you don't use this bedroom much, you might want to restrict the incoming air at the duct in this room and/or open wider the vents on other rooms to decrease the pressure in the a/c vents and balance the heating and cooling.
If you use this room a lot and need this amount of airflow in, you might consider cutting 1/4 inch off the bottom of the door to allow more flow out of the room. I installed new oak doors on the bedrooms in our house and I erred on the side of leaving the doors too close to the tile floor. This means I have to carefully balance the restriction louvers on the air ducts to avoid pressurizing a particular room.
If there is insufficient space under the door the room may become pressurized and if there is a bathroom off the bedroom you may lose conditioned air through the exhaust vent in the bathroom.
Edit: I now think from the comments and answers that a whole bedroom could not be pressurized enough to force any significant air out the bathroom vent.
As far as "practical effects" goes, the amount of heated (cooled) air going through this room is less than it would otherwise be. This could affect appliance life since it would run longer/more to get the room to temperature, depending on the magnitude of the change of course!
You could freeze your AC coil or trip your furnace out on over heat, due to lack of air flow. As far as humans are concerned, there is no concern.
The air will want to move through the path of least resistance. If you block the exits of a room off, it would have the same effect as blocking off the entrance of the air into the room. This will result in the positive pressure, but also no additional airflow into the room as the air will flow into other rooms that have return.
This could result in the room being cold because no additional air would be flowing into it.
I think people are overlooking the more significant issue of any kind of pressure imbalance in a heated or cooled house - condensation.
If a room is hot and forcing air into non-desirable spaces (cracks in the wall or ceiling for example) the drastic change in temperature along surfaces can cause condensation in areas that should be dry. This is a problem in humid environments especially.
Health wise - no issue. A house isn't sealed well enough to build up significant pressure, nor would an air pump keep working in the pressure was too high.
On the plus side - you shouldn't be getting many flies or mosquitos in the room.
